Hydraulic jarring tool for use in wells



Sept. 3, 1968 a. Q. HARRINGTON 3,399,740

HYDRAULIC JARRING TOOL FOR USE IN WELLS 5 Sheets-Sheet 1 Filed Aug. 18, 1966 INVENTOR BURCHUS 0. BARRINGTON g u A'uf 9M ,2

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u/ F m m Se t. 3, 1968 B. Q. BARRINGTON HYDRAULIC JARRING TOOL FOR USE IN WELLS Filed Aug. 18, 1966 ATTORNEYS Se t. 3, 1968 5. BARRINGTON 3,399,740

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United States Patent 3,399,740 HYDRAULIC J ARRING TOOL FOR USE IN WELLS Burchus Q. Barrington, Duncan, 0kla., assignor to Halliburton Company, Duncan, Okla, a corporation of Delaware Filed Aug. 18, 1966, Ser. No. 573,312 6 Claims. (Cl. 175297) ABSTRACT OF THE DISCLOSURE A jarring tool including a frustoconical collar supported for axial sliding movement between abutments of a mandrel. The collar, when spaced from the mandrel, defines a flow-restricting passageway operable to impede mandrel movement. Moving the collar axially along the mandrel changes the flow capacity of the passageway.

General background of the invention This invention relates to an apparatus for use in wells. In particular, it relates to a hydraulic jarring tool which may be effectively employed to facilitate movement of articles which become stuck within well bores.

In perforating drilling and completion operations in oil fields, operators occasionally encounter the necessity of moving articles which have become stuck in a well bore. At times, for example, a packer on a testing tool may stick or fail to release so as to make its removal inordinately diflicult.

When this happens a jarring tool may be employed to facilitate the release of the stuck article. Jarring tools may be incorporated in strings supporting articles which are likely to become stuck or they may be subsequently incorporated in conduit strings which are attached to articles stuck in a well bore by following conventional well fishing techniques.

A variety of hydraulic jarring tools have heretofore been provided. In general, these tools have been characterized by flow impeding devices which are carried by movable components of the tools and which are operable for a limited initial portion of the travel or movement of the movable components. This enables an upward strain to be placed on a movable component of a tool, with the movement impeding mechanism initially resisting upward movement of the movable component, while a fixed component of the tool is anchored to the stuck article.

Repeated reciprocation of the movable component serves to impart repeated jars to the stuck article which ultimately effect the release of the article.

All too often, hydraulic jarring tools previously devised have been characterized by structural complexities which often created as many problems as the tools solved. Many such tools utilized multiple valve arrangements, orifice passages, or ground sea-t closures for valves, all of which created significant operational problems. Multiple valve arrangements and orifice systems in impedance devices are vulnerable to clogging and failure during operation. The use of ground seat valving devices introduces vulnerability to seat scoring and ultimate tool failure.

Some hydraulic jars have been characterized by the maintenance of the same diameter of internal portions. This restricting structural arrangement introduces structural complexities which are neither necessary nor significant in the effective operation of hydraulic jar tools.

General objects and summary of invention All of the conventional engineering arrangements above discussed engender fabrication or operational dif- "ice ficulties and limitations which are desirable to avoid. For this reason it is an object of the present invention to provide an improved hydraulic jar tool which is characterized by a radically new and simplified flow impedance mechanism.

It is a particular object of the invention to provide a flow impedance device for use in a well tool which is charatcerized by flow impeding passage means having an axially varying, cross-sectional area.

It is a further object of the invention to provide such an improved flow impedance device which avoids the resort to valve arrangements and which utilizes a single, unvalved flow restricting passage, the flow capacity of which varies depending upon the direction of movement of the flow impeding device.

It is another object of the invention to provide such an improved well tool mechanism including a self-flushing or cleaning flow impeding passage.

It is likewise an object of the invention to provide such an improved device including a unique mechanism for selectively adjusting the minimum flow capacity of the flow restricting passage means and which does not affect the distance of impeded movement between movable components of the tool.

In order to accomplish at least some of the foregoing objectives there is presented through the invention a well tool including a first component and a second component, axially movable relative to the first component. The tool further includes fiuid reservoir means and movement impedance means carried by the second component. This movement impedance itself comprises an assembly movable through the reservoir means of the tool. The assembly has wall means extending transversely of the reservoir means and sealingly engaging portions of the first component and further includes passage means extending through the wall means to communicate with opposite axial sides of the wall means. The characterizing feature of the combination resides in the unique structure of the passage means which provides a progressively axially varying cross-sectional area.

A particularly significant facet of the invention resides in a passage means configuration which is generally annular and frustoconical and coaxially aligned with the movement axis of the second component. In the optimum form of the invention, the wall means of the assembly means includes an axially movable portion which is adapted to effect an increase in the width of the annular, frustoconical passage means in response to axial movement of the portion in the direction of the convergence of the frustoconical passage.

Drawings of preferred embodiment In describing the invention reference will be made to a preferred embodiment illustrated in the appended drawings.

In the drawings:

FIGURE 1 schematically illustrates the hydraulic jarring tool of the present invention positioned in a well bore to facilitate the release of a stuck packer;

FIGURES 2a through 2] provide fragmentary. vertically sectioned, and enlarged views of the generally cylindrical components of the FIGURE 1 assembly correlating with axial sections of the tool as shown in FIGURE 1;

FIGURE 3 provides a transverse sectional view of a portion of the tool as viewed along the section line 3-3 of FIGURE 2b and illustrating structural details of a splined interconnection between relatively movable mandrel and barrel components of the tool;

FIGURE 4 provides a transverse sectional view through a portion of the tool as viewed along the section line 4-4 of FIGURE 2d and illustrating radial flow passages formed in upper abutment means carried by the mandrel which provide fluid communication between reservoir means of the tool and a restricted flow passage of a movement impedance device;

FIGURE provides a transverse sectional view through the FIGURE 1 apparatus as viewed along the section line 55 of FIGURE 2d and illustrating a generally annular, frustoconical flow passage of the flow impedance device of the FIGURE 1 tool, which flow passage varies in effective cross-sectional area axially of the tool by decreasing in a progressively axial fashion in the direction of the lifting force exerted on the mandrel component of the tool which supports this passage;

FIGURE 6 provides a transverse sectional view of the FIGURE 1 tool as viewed along the section line 66 of FIGURE 2d and illustrating radial flow passages in lower abutment means carried by the tool mandrel and which provide fluid communication between the tool fluid reservoir and the lower end of the axially varying flow restricting passage of the tool;

FIGURE 7 provides a transverse sectional view of the FIGURE 1 tool as viewed along the section line 77 of FIGURE 2e and illustrates tool receiving sockets which enable the threadably mounted lower abutment means of the mandrel of FIGURE 1 tool to be adjusted in axial position; and

FIGURE 8 provides an enlarged fragmentary peripheral view of the portion of the FIGURE 1 tool as viewed in the general view direction 88 of FIGURE 2e and illustrating structural details of a yieldable detent mechanism which serves to secure the lower abutment means of the mandrel in a selected position of axial adjustment.

The overall structure FIGURE 1 schematically illustrates a conventional installation including a conduit string 1 extending into a well bore 2. A packer 3 is supported on the lower end of the string 1 and for the purpose of this disclosure is shown as being expanded and in stuck engagement with a wall 4 of the well 2.

Conduit string 1 includes a hydraulic jar 5 interposed in the string above the stuck packer 3. Jar 5 may have been initially included in the string or may have been subsequently connected with the packer 3 through conventional well fishing techniques. For example, an operator may have discovered the stuck condition of the packer 3 and separated the upper portion of a conduit string formerly supporting the packer 3 from this packer as, for example, at a conventional safety joint 6. After the initial string was removed, the jar 5 could have been inserted in the lower end of the removed string and the 1 string then relowered with a conventional coupling at its lower end which was mateable with the safety joint 6 so as to reattach the string to the stuck anchor 3.

As generally shown in FIGURES 1 and 2a through 2 hydraulic jar 5 includes, as its basic components, a mandrel 7 threadably connected with the portion of the conduit string 1 extending upwardly from the jar 5. Hydraulic jar 5 also includes a barrel component 8 which :may be fabricated from a plurality of threadably interconnected cylindrical components 8a, 8b and 8c. Barrel 8 may be threadably connected to safety joint 6 so as to be anchored to the stuck packer 3.

Mandrel 7 itself may be fabricated from a plurality of threadably interconnected components 7a, 7b and 70. Component 7a at its upper end includes a conventional, female threaded coupling 9 which is connected to a conventional, threaded male fitting in the conduit string 1. As illustrated, mandrel 7 is generally tubular or cylindrical in character and telescopingly received Within the barrel 8.

Section 8c of barrel 8, as shown in FIGURE 2f, may be provided with a conventional threaded male fitting 10 for effecting threaded engagement with the stuck article 3 through the interposed safety joint 6 of FIGURE 1.

A generally annular, hydraulic fluid reservoir 11 is carried within the hydraulic jar 5 between outer and inner walls respectively of mandrel 7 and barrel 8. The upper and lower limits of this reservoir may be defined by conventional, axially spaced, annular seals 12 and 13 carried by the barrel 8. Mandrel portion 7b includes a cylindrical outer periphery 14 disposed in slidably and sealing engagement with seal 12. Mandrel section 70 includes an outer cylindrical peripheral wall 15 disposed in slidable and sealing engagement with the seals 13.

In order to enable the hydraulic coupling 5 to transmit rotary force or torque, the mandrel 7 is splined to the barrel 8. This conventional interconnection, as shown in FIGURES 2b and 20, may comprise a plurality of longitudinal ridges or splines 16 carried by and circumferentially spaced about the outer periphery of the mandrel section 7b. Each of the splines 16 is slidably received within a radially recessed and longitudinally extending groove 17 formed on the inner periphery of the barrel section 8b.

Barrel section 8a, at its lower end, provides an annular anvil face 18. Mandrel section 711 carries a radially outwardly extending annular hammer face 19 which is disposed beneath the anvil face 18. With the mandrel 7 fully converged with the barrel 8, as shown in FIGURES 2a through 2], the hammer 19 is spaced beneath the anvil 18 but is movable upwardly into engagement with the anvil 18 through an annular portion 11a of the fluid reservoir 11.

Movement impedance device FIGURES 2d and 2e illustrate stuuctural details of a movement impedance device 20 which is disposed for axial travel within the fluid reservoir 11 and which is carried by the mandrel 7.

Impedance 20 includes a frustoconical, upwardly converging shoulder 21 carried by the mandrel section 7c. Assembly 20 includes a collar 22 having a frustoconical inner face 23 and a generally cylindrical outer face 24. Outer face 24 is slidably and sealingly receivable within a cylinder wall portion 25 of barrel section 8b. Frustoconical wall 23 of collar 22 faces and is mateable with the outer periphery 21a of shoulder 21.

A first, generally annular abutment 26 is carried by the mandrel section 7b above shoulder 21 as generally shown in FIGURE 2d. The lower end of abutment 26 is defined by a plurality of circumferentially spaced teeth 27 which alternate with a plurality of passages 28. Each passage extends longitudinally upwardly into the lower end of the abutment 26 and extends radially between an annular passage 29 and the outer periphery 30 of the abutment 26 which is spaced radially inwardly from the cylindrical wall 25. Recess 29 may comprise an annular groove formed on the outer periphery of the mandrel section 70 immediately above the frustoconical Wall 21a of the shoulder 21.

Anotlher annular abutment 31 is disposed beneath the shoulder 21 and the collar 22. Abutment 31 comprises a sleeve 32 connected by a conventional threaded connection 33 to the outer periphery of the mandrel section 7c. The upper end of abutment 31 includes a plurality of longitudinally projecting, circumferentially spaced teeth 34. Alternating with teeth 34 are a plurality of circumferentially spaced passages 35, Spaced passages 35 extend radially outwardly from an annular passage 36. As illustrated, passage 36 may comprise an annular recess formed on the outer periphery of the mandrel section and which extends longitudinally from the frustoconical face 21a downwardly to extend longitudinally past and radially within the radial passages 35. Thus, passages 35 provide fluid communication between the annular recess 36 and the outer periphery 37 of the sleeve 32, which periphery is spaced radially inwardly from the cylindrical wall 25.

As illustrated, collar 22 is axially slidable between the abutment extremities as defined by the lower ends of the from the mating frustoconical shoulder wall 21a so as to define a flow restricting passage 38. Flow restricting passage 38 is generally annular and frustoconical is configuration and decreases in cross-sectional area in a generally upward direction, i.e., the direction in which movement of the mandrel 7 is to be initially impeded.

When collar 22 is disposed in its uppermost position, i.e., in engagement with the lower extremities of the teeth 27, the width of the passage 38 will be substantially increased. Thus between the lower and upper positions of the collar 22, the flow capacity or effective width w of the passage 38 will progressively increase such that the flow capacity of the passage will progressively increase.

Immediately above cylinder wall 25 is an enlarged barrel chamber 39 defined by a generally cylindrical wall 40 having a diameter exceeding that of the wall 25. The axial extent of the wall 40 substantially exceeds the axial distance required to move the mandrel 7 from its illustrated position of convergence with the barrel 8 to a position suflicient to bring the collar 22 fully into radial juxtaposition with the chamber 39. When the collar 22 is positioned in the chamber 39, the cylindrical wall 24 is spaced radially inwardly from the wall 40.

The initial or lower position of the collar 22 relative to the shoulder 20 is determined by the axial position of the threaded sleeve 32 in relation to the mandrel section 7c. By turning the sleeve 32 so as to advance it upwardly on the threaded coupling 33 the collar 22 will be raised so as to increase the width w of the flow restricting passage 38. Conversely, of course, threaded downward movement of the sleeve 32 will serve to lower the collar 22 relative to the shoulder 21 and thus decrease the width and crosssectional area of the passage 38.

The sleeve 32 may be secured in selected positions of threaded adjustment by a yieldably releasable, detent mechanism 41. Mechanism 41 comprises a series of circumferentially spaced, longitudinally extending recesses 42 formed on the outer periphery of the mandrel section 7c immediately beneath the coupling zone 33. Mechanism 41 additionally includes a resilient, split ring 43 self grippingly secured in an annular groove 44 formed on the lower end of the sleeve 32, and having one of its two free ends yieldably engageable with the recess 42. Thus, as shown in FIGURE 2e, this one free end 45 may extend generally radially from the ring groove 44 through a radial opening 46 in the sleeve 32 so as to extend from the groove 44 fully through the sleeve and into detenting engagement with a groove 42 of the sleeve section 70. Thus, by rotating the sleeve 32 the yieldable detent finger 45 will be deflected from one groove 42 to another. With this arrangement the sleeve 32 may be secured at any of a series of incremental rotary positions determined by the sequential detenting engagement of the finger 44 with the recesses 42. Sleeve 32 may include a radially extending screw driver recess 47 and socket wrench engaging teeth 48 and recesses 49 to facilitate engagement of the sleeve with tools for effecting its rotation.

Operation of movement impedance device With the tool components disposed as shown in FIG- URES 2d and 2e, an upward lifting force is exerted on the string 1. Resistance to upward movement of the mandrel 7 is provided by the movement impedance device which is fully immersed and axially movable through the fluid body which fills the fluid reservoir 11. This movement impedance results from the relatively small flow capacity of the frustoconical passage 38 when the collar 22 is supported in its lower position on the abutment 31.

The movement impedance effect .of the small flow passage 38 continues until the collar 22 and shoulder 21 are moved fully into the enlarged chamber 39. At this point, movement of fluid within the reservoir 11 downwardly past the movement impedance device 20, so as to permit upward movement of the mandrel 7, is greatly facilitated. This facilitation results from an annular bypass passage which then exists between the wall 40 and the collar wall 24 and which enables fluid to move downwardly around the outside of the collar 22 and elfectively bypass the flow restricting passage 38. Thus, when the collar 22 is moved into the chamber 39, the flow impedance effect of the mechanism 20 is interrupted and the mandrel 7 may then undergo abrupt upward movement. This abrupt upward movement results from the interruption of the impedance effect of the mechanism 20, in conjunction with the prior stretching or tensioning of the mandrel 7 which occurred while trying to lift the mandrel 7 against the full impeding resistance afforded by the mechanism 20. As a result of this rapid upward movement of the mandrel 7, the hammer face 19 is brought into abrupt engagement with the anvil face 18 and an upward jar or force is imparted to the stuck article 3.

After this jarring force has been imparted, the upper portion of the string 1 is then relowered so as to move the mandrel 7 downwardly back into converged relation with the barrel 8. During this downward movement, while the collar 22 is within the chamber 39, fluid within the reservoir 11 may flow upward around the collar 22 both between the walls 39 and 24 and through the passage 38. On this downward stroke of the mandrel 7 the collar 22 will be held upwardly against the abutment 26 because of fluid resistance to its downward movement so as to cause the effective enlargement of the passage 38. As a consequence of the increase in size of the pas- 1 sage 38, and the bypass channel around the outer periphery of the sleeve 22, downward movement of the assembly 20 through the chamber 29 is vastly facilitated.

When the collar 22 has moved ipto slidable engagement with the cylinder 25 so as to substantially-prevent bypassing flow around the outsidenoif the onar zz, fluid flow upwardly to assembly 20 still occurs ata relatively high flow rate. This high flow rate results from the enlarged size of the passage 38 which isfacoiisequence of the collar 22 being in its uppermost position, i.e., engaged with the abutment 26. With the elements'returned to their initial position as illustrated in FIGURES ZbthrOugh 2f, the cycle may then be sequentially repeatedso as to impart further jarring forces to the stuck article 3.

Significantly, during the upward movement of the mandrel 7, the flow passage 38 progressively enlarges in the direction of fluid flow as a consequence of the frustoconi: cal and downwardly diverging character of this passage. With this constantly or progressively enlarging flow impeding passage, the likelihood of passage clogging is substantially diminished. The flow of fluid downwardly through the passage becomes progressively easier as the area available for flow progressively increases.

The enlargement in size of the passage 38, resulting from axial movement of the sleeve 22 facilitates, effective, complete, and overall flushing of the passage 38 on downstrokes of the mandrel 7.

Advantages and scope of the invention A prime advantage of the invention resides in the consistently effective and virtually non-cloggable character of the flow impedance device. The progressively enlarging character of the flow impeding passage in the direction of fluid flow, when the impedance device is resisting mandrel movement, effectively minimizes the likelihood of clogging.

The manner in which the flow impeding passage changes considerably in size between up and down strokes of the mandrel causes the passage to be effectively flushed between each impedance stroke.

The adjusting device enables the time of the impedance stroke to be selectively adjusted without changing the length of the mandrel stroke. In other words, as the size of the passage 38 is decreased by adjusting the position of the collar 32 the time duration of the impedance up stroke is increased. This enables a tool to be adjusted to change the duration of an impedance stroke without creating the complication of adjusting the length of the mandrel stroke.

The tool is able to operate effectively with every major internal segment of the barrel having a different diameter. Thus, the diameter of the cylinder is substantially smaller than the diameter of the enlarged chamber 39 and the diameter of the barrel 8 in the vicinity of the spline grooves 17 differs substantially from the diameter of either the passage 39 or the cylinder wall 25.

It is especially noteworthy that the flow impedance mechanism 20 operates without the impediment of valve orifices, valve seats, plural valve arrangements, etc. Flow is controlled through the simple utilization of the frustoconical passage 38 which is continuously open and automatically changes in size, depending upon the direction of mandrel stroke. Valving at either lower or upper ends of the collar 22 is effectively avoided by reliance on the non-impeding flow passages 28 and 35. As will be appreciated, passages 28 and in no way regulate flow through the impedance device, since this flow regulation is achieved entirely through the variable, frustoconical flow passage 38.

In maintaining the mandrel splines fully axially displaced from the mandrel hammer, there are no problems engendered with respect to transmitting hammer force to the mandrel splines which would result by attempting to integrate these components.

In describing the invention reference has been made to a preferred embodiment. However, those skilled in the well tool art and familiar with the disclosure of this invention may envision additions, deletions, substitutions, or other modifications which would fall within the purview of the invention as defined in the appended claims.

I claim:

1. In a well tool, a combination comprising:

a first component;

a second component having a longitudinal axis, said second component being movable relative to said first component along said longitudinal axis;

fluid reservoir means;

movement impedance means carried by said second component and movable through said reservoir means along said longitudinal axis of said second component;

first wall means carried by said movement impedance means;

second wall means carried by said movement impedance means and disposed adjacent said first wall means;

at least one of said wall means having at least a portion generally inclined relative to the longitudinal axis of said second component and operable, in combination with the other of said wall means, to define a generally converging restricted passage means adjacent said inclined portion and including a first portion having a first cross-sectional area;

and

a second portion displaced from said first portion along the path of flow of fluid through said restricted passage means and having a second cross-sectional area smaller than said first cross-sectional area; and

seal means carried by said second component and operable, in combination with said restricted passage means, to cause said restricted passage means to impede movement of said second component within said reservoir means along said longitudinal axis.

2. In a well tool, a combination comprising:

a first component;

a second component axially movable relative to said first component;

fluid reservoir means;

movement impedance means carried by said second component and movable through said reservoir means;

said movement impedance means having wall means defining restricted passage means and operable to cause fluid to flow therethrough from a portion of said reservoir means in advance of said second component, when said second component is in motion, to a portion trailing said moving second portion and thereby impede movement of said second component through said fluid reservoir means;

said wall means of said movement impedance means including a wall portion reciprocable along an axis in response to the pressure of fluid within said reservoir means, said movable wall portion extending generally transversely of said axis, and said transverse and movable wall portion being operable to effect a decrease in width of said restricted passage means in response to movement of said wall portion in one direction along said axis; and

spaced abutment means carried by said movement impedance means, said spaced abutment means being displaced along said axis of reciprocation of said transverse and movable wall portion and operable to define the extremities of reciprocating movement of said wall portion; and

one of said abutment means being disposed ahead of said transverse and movable wall portion in said one direction and adjustable in position along said axis of reciprocation of said transverse and movable wall portion.

3. In a well tool, a combination comprising:

a first component;

a second component axially movable relative to said first component;

fluid reservoir means; and

movement impedance means carried by said second component and comprising an assembly movable through said reservoir means;

said assembly having wall means defining a generally annular and frustoconical passage means operable to cause fluid to flow therethrough from a portion of said reservoir means in advance of said second component, when said second component is in motion, to a portion trailing said moving second portion and thereby impede movement of said second component through said fluid reservoir means;

said passage means progressively varying in crosssectional area along the general direction of fluid flow therethrough.

4. In a well tool, a combination comprising:

a first component;

a second component axially movable relative to said first component;

fluid reservoir means; and

movement impedance means carried by said second component and comprising an assembly movable through said reservoir means;

said assembly having wall means defining a generally annular and frustoconical passage means converging in one direction and operable to cause fluid to flow therethrough from a portion of said reservoir means in advance of said second component, when said second component is in motion, to a portion trailing said moving second portion and thereby impede movement of said second component through said fluid reservoir means;

said passage means progressively varying in crosssectional area along the general direction of fluid flow therethrough;

said wall means of said assembly means including an axially movable portion operable to eifect an increase in width of said generally annular and frustoconical passage means in response to axial movement of said portion in the direction of convergence of said passage means.

5. A hydraulic jarring tool for use in a well, said tool comprising:

mandrel means;

barrel means telescopingly receiving said mandrel means;

frustoconical shoulder means carried on said mandrel means;

a collar having a frustoconical inner wall and a cylindrical outer wall, with the inner wall facing said frustoconical shoulder means, said inner wall of said collar having a configuration conforming with the outer periphery of said frustoconical shoulder means;

axially spaced, first and second abutment means carried by said mandrel means and disposed on opposite axial sides of said frustoconical shoulder means and supporting said collar for limited axial movement relative to said frustoconical shoulder means, with the inner wall of said collar being radially spaced from said shoulder means while in engagement with one of said abutment means;

cylinder means carried by said barrel means adapted to telescopingly and slidably receive the outer wall of said collar;

wall means defining a chamber axially adjacent said cylinder means, said wall means having at least a portion spaced from the outer wall of said collar when said collar is radially adjacent thereto and de fining with said outer Wall a flow passage extending fully axially of said collar;

fluid reservoir means including said cylinder means and said chamber with said shoulder means and collar being axially movable therewithin;

said inner wall of said axially movable collar cooperating with said frustoconical shoulder means to define a variable capacity flow passage of axially progressive, varying capacity; and

means providing fluid communication between each of the opposite axial ends of said variable capacity passage and said fluid reservoir means.

6. A hydraulic jarring tool for use in a 'well, said tool comprising:

mandrel means;

barrel means telescopingly receiving said mandrel means;

frustoconical shoulder means carried on said mandrel means;

a collar having a frustoconical inner wall and a cylindrical outer wall, with the inner wall facing said frustoconical shoulder means, said inner wall of said collar having a configuration conforming with the outer periphery of said frustoconical shoulder means;

axially spaced, first and second abutment means carried by said mandrel means and disposed on opposite axial sides of said frustoconical shoulder means and supporting said collar for limited axial movement relative to said frustoconical shoulder means, with the inner wall of said collar being radially spaced from said shoulder means while in engagement with one of said abutment means;-

cylinder means carried by said barrel means adapted to telescopingly and slidably receive the outer wall of said collar;

wall means defining a chamber axially adjacent said cylinder means, said wall means having at least a portion spaced from the outer wall of said collar when said collar is radially adjacent thereto and defining with said outer wall a flow passage extending fully axially of said collar;

fluid reservoir means including said cylinder means and said chamber with said shoulder means and collar being axially movable therewithin;

said inner wall of said axially movable collar cooperating with said frustoconical shoulder means to define a variable capacity flow passage of axially progressive varying capacity; and

means providing fluid communication between each of the opposite axial ends of said variable capacity passage and said fluid reservoir means, and comprising, on each abutment means,

a plurality of radial pas-sages extending axially inward from the end of each abutment facing said collar, and

an annular recess formed on said mandrel means between said shoulder means and said abutment means,

said radial passages providing fluid communication between said reservoir means and said annular recess,

said one abutment means being engageable with the end of said collar having the larger diametered portion of the inner wall thereof; and

said one abutment means comprising:

a sleeve threadably mounted on said mandrel means,

the outer periphery of said sleeve being receivable within said cylinder means but radially spaced therefrom when so received,

a plurality of recesses carried by and spaced circumferentially about said mandrel means, and

yieldable detent means carried by said sleeve and releasably engageable with said recesses.

References Cited UNITED STATES PATENTS 2,828,822 4/1958 Greer ----297 2,896,917 7/1959 McGarrahan 175-297 3,088,533 5/1963 Sutlifi 175-297 3,221,826 12/1965 Webb 175-297 JAMES A. LEPPINK, Primary Examiner. 

